Main thing I remember is that it was one of the first players which could scan its files for iD3 tags and sort them into a database, without need for any PC app. Drag drop done. Sansa Clip series works in a similar fashion.

The one I have now needed a new HD and I had a spare leftover from a Rio Karma mod. To disassemble you will need a T6 Torx Security (tamper proof) bit for the 2 screws on the bottom edge. $3 on eBay. Remove those and crack the case like an iPod at the seams.

The back half of the player will pop off in one piece. With the screen face down on a table, the battery is the top layer, followed by a Hitachi 1.8-inch 20gb hard drive, then the mainboard. Unfortunately RCA made it a real PITA to replace the drive. The bottom side of the HD is wrapped in a layer of copper sheeting which is stuck to it with something really sticky. There's padding on the bottom of the copper layer so it doesn't touch the mainboard. It has flaps that go over the edges and a bit onto the front side of the drive. Hard to peel off and easy to tear.

The battery is wired to the copper (top edge), and there's another wire from the copper sheet to the mainboard (side edge). Why they didn't run a wire directly from the mainboard to the battery, I'm not sure. Leads are soldered too, no easy-to-remove plug for the battery.

Once you get it off, move the copper layer to the side (wires still attached to battery and mainboard, hopefully) and pull out the drive. With the replacement, restick the copper sheet to it, and insert the drive into the 44 pin IDE connector.